The Spatial and Temporal Expression Patterns of Integrin α9β1 and One of Its Ligands, the EIIIA Segment of Fibronectin, in Cutaneous Wound Healing

The fibronectins (FN) comprise a family of adhesive extracellular matrix proteins thought to mediate important functions in cutaneous wounds. Plasma fibronectin (pFN) extravasates for days from intact hyperpermeable vessels following injury whereas mRNAs encoding the cellular fibronectins (cFN) that include two segments, termed EIIIA (EDA) and EIIIB (EDB), are expressed by wound cells. Wounds in mice null for pFN appear to heal normally whereas those in EIIIA null mice exhibit defects, suggesting that cFN may play a role when pFN is missing. Integrin α9β1, a receptor for several extracellular matrix proteins as well as the EIIIA segment, is expressed normally in the basal layer of squamous epithelia. We report results from immunohistochemistry on healing wounds demonstrating that EIIIA-containing cFN are deposited abundantly but transiently from day 4 to 7 whereas EIIIB-containing cFN persist at least through day 14. Elevated expression of α9β1 is seen in basal and suprabasal epidermal keratinocytes in wounds. The spatial expression patterns of cFN and α9β1 are distinct, but overlap in the dermal–epidermal junction, and both are expressed contemporaneously. These observations suggest a role for α9β1–EIIIA interactions in wound keratinocyte function

Integrin Regulation of CAF Differentiation and Function

Extensive remodeling of the extracellular matrix, together with paracrine communication between tumor cells and stromal cells, contribute to an “activated” tumor microenvironment that supports malignant growth and progression. These stromal cells include inflammatory cells, endothelial cells, and cancer-associated fibroblasts (CAFs). Integrins are expressed on all tumor and stromal cell types where they regulate both cell adhesion and bidirectional signal transduction across the cell membrane. In this capacity, integrins control pro-tumorigenic cell autonomous functions such as growth and survival, as well as paracrine crosstalk between tumor cells and stromal cells. The myofibroblast-like properties of cancer-associated fibroblasts (CAFs), such as robust contractility and extracellular matrix (ECM) deposition, allow them to generate both chemical and mechanical signals that support invasive tumor growth. In this review, we discuss the roles of integrins in regulating the ability of CAFs to generate and respond to extracellular cues in the tumor microenvironment. Since functions of specific integrins in CAFs are only beginning to emerge, we take advantage of a more extensive literature on how integrins regulate wound myofibroblast differentiation and function, as some of these integrin functions are likely to extrapolate to CAFs within the tumor microenvironment. In addition, we discuss the roles that integrins play in controlling paracrine signals that emanate from epithelial/tumor cells to stimulate fibroblasts/CAFs

Hic-5 promotes the hypertrophic scar myofibroblast phenotype by regulating the TGF-beta1 autocrine loop

Following severe traumatic or thermal injury to the dermis, hypertrophic scars (HTSs) often develop in humans. These scar fibroblasts (hypertrophic scar fibroblasts (HTSFs)) retain the myofibroblast phenotype persistently, rather than transiently as in acute wounds. These pathogenic myofibroblasts constitutively express smooth-muscle cell alpha-actin (SMAA), deposit an excessive amount of extracellular matrix (ECM) proteins, are highly contractile, and stably display large focal adhesions. Increasing evidence supports a mechanism in which autocrine production and activation of transforming growth factor-beta1 (TGF-beta1) are required to maintain the pathogenic myofibroblast phenotype. We recently reported that Hic-5, a focal adhesion protein that is upregulated by TGF-beta1, is expressed persistently in HTSF compared to normal adult fibroblasts (NADFs). We now find that Hic-5 is an important regulator of the constitutive myofibroblast phenotype in HTSFs. Silencing the expression of Hic-5 in HTSFs with specific siRNAs dramatically reduces TGF-beta1 production, decreases the generation of supermature focal adhesions reduces expression of SMAA and decreases collagen contraction and ECM synthesis. Our findings demonstrate that Hic-5 is an essential component of the mechanism regulating autocrine production of TGF-beta1 and the resulting pathogenic myofibroblast phenotyp

TGF-beta1 slows the growth of pathogenic myofibroblasts through a mechanism requiring the focal adhesion protein, Hic-5

Pathogenic scarring is a devastating disorder that impairs normal tissue function after injury. Differentiated myofibroblasts deposit and organize scars over a continuum, from normal to pathogenic, and yet the mechanisms regulating their appearance and disappearance from tissues are enigmatic. We reported previously that key functions of myofibroblasts derived from hypertrophic scars (HTSF) are constitutively activated by an autocrine loop involving transforming growth factor-beta1 (TGF-beta1). We now report that this autocrine induction of TGF-beta1 results in a constitutively high level of Hic-5, which markedly reduces HTSF proliferation relative to normal adult human dermal fibroblasts (NADF) without changing apoptosis. Cyclin D1 and A levels are constitutively lower in HTSF compared to NADF, and the cyclin-dependent kinase inhibitor p21(cip1) is upregulated in HTSF and located in the nucleus. Inhibition of autocrine TGF-beta1 production in HTSF reverses this process, lowering Hic-5 and p21(cip1) levels and increasing replication. Moreover, Hic-5 is partially localized in the nucleus of HTSF, and knocking down Hic-5 with specific siRNAs in these cells results in decreased p21(cip1) levels and a concomitant increase in proliferation. Our findings show that autocrine production of TGF-beta1 upregulates the expression of Hic-5, which is essential for perpetuating the decreased proliferation seen in this pathogenic myofibroblast

Streptococcal Collagen-like Protein 1 Binds Wound Fibronectin: Implications in Pathogen Targeting

Group A Streptococcus (GAS) infections are responsible for significant morbidity and mortality worldwide. The outlook for an effective global vaccine is reduced because of significant antigenic variation among GAS strains worldwide. Other challenges in GAS therapy include the lack of common access to antibiotics in developing countries, as well as allergy to and treatment failures with penicillin and increasing erythromycin resistance in the industrialized world. At the portal of entry, GAS binds to newly deposited extracellular matrix, which is rich in cellular fibronectin isoforms with extra domain A (EDA, also termed EIIIA) via the surface adhesin, the streptococcal collagen-like protein 1 (Scl1). Recombinant Scl1 constructs, derived from diverse GAS strains, bind the EDA loop segment situated between the C and C' β-strands. Despite the sequence diversity in Scl1 proteins, multiple sequence alignments and secondary structure predictions of Scl1 variants, as well as crystallography and homology modeling studies, point to a conserved mechanism of Scl1-EDA binding. We propose that targeting this interaction may prevent the progression of infection. A synthetic cyclic peptide, derived from the EDA C-C' loop, binds to recombinant Scl1 with a micromolar dissociation constant. This review highlights the current concept of EDA binding to Scl1 and provides incentives to exploit this binding to treat GAS infections and wound colonization